Bias roll transfer

ABSTRACT

A biasable transfer member is herein disclosed suitable for use in transferring xerographic images from a photoconductor to a final support sheet. The member is adapted to electrically cooperate with the photoconductor to establish a directional force field therebetween capable of attracting toner from the photoconductor toward the member and features a structure which provides for a more efficient transfer operation while at the same time accurately matching the speed of the support sheet to the photoconductor.

United States Patent Dolcimascolo et al.

1451' Nov, 7, 1972 [54] BIAS ROLL TRANSFER I [72] Inventors: CharlesDolclmascolo, 'Fairport;

Daniel S. Hoffman; Hugh L. Jones, both of Rochester; James E. Mercik,

Webster, all of NY.

[731 Assignee: Xerox Corporation, Stamford,

- Conn. 2

[22] Filed: Dec. 23, 1970 [21] Appl. No.: 100,969

1521 11.5. C1. ..346/74 Es, 101/13,:155/3 [51] Int. Cl.....G03g 15/04,G03g 15/08,;G03g 15/16 [58] Field of Search..346/74 ES; lO1/DIG. 13;355/3 I [56] References Cited UNITED STATES/PATENTS 3,281,857 10/1966Kaiser ..346/74 ES 3,441,938

4/1969 Markgraf ..346/74 ES 3,285,168 11/1966 Childress ..l01/D1G. 13

3,316,555 I 4/1967 Barish ..346/74 ES. 3,534,383 10/1970 Tsukatani..346/74 ES Primary Examiner-Howard W. Britton Attorney-James J.Ralabate, Donald F. Daley and Thomas J. Wall 1571- ABSTRACT A biasabletransfer member is herein disclosed suitable for use in transferringxerographic images from a photoconductor to a final support sheet; Themember is adapted to electrically cooperate with the photoconductor toestablish a directional force field therebetween capable of attractingtoner from the photoconductor toward the member and features a structurewhich provides for a more efficient transfer operation while at the sametime accurately matching the speed of the support sheet to thephotoconductor.

11 Claims, 3 Drawing Figures PATENTEDNUY 1 I972 $702,482

' sum 2 BF 2 FIG? as as as I 32 I 68 Mtg. I

, duplexingprocesses.v

11 Bus Ron. I

t. Thisinvention relates to xerography and, in particu- I lar, toapparatus for transferring xerographic toner 1 images from one supportsurface to another. In conventional xerography, atphotosensitive plate,which consists ofv a photoconductive coating placed 2 over aconductivebacking ischarged uniformly. and the charge plate then exposedto a light image of an 1 original. Under the influence of. the lightimage, the

charge on the plate is selectively, dissipated to record 1 the originalinput scene information on the plate in the 'form of a latentelectrostatic image. The latent image is developed, or made visible, nby .1 applying oppositely 5 charged toner particles to the plate surfacein a manner sothatthe toner particles are attracted into the imagedareas. The developed images are generally transferred from thephotoconductor to a final support material, such as paper or the like,and affixed thereto to form a r permanent record of the original.

I-Ieretofor', image transfer was generally accom- -.plish ed by means ofcorona induction using a corona generator similar to that disclosed byVyverberg in U.

S P-at. No. 2,836,725: In corona induced transfer, the

- final support sheet isplaced in direct contact with the toner imagewhile the. image is supported on the y. photoconductive surface. Theback of the sheet, that is, the side away from theimage, is sprayed witha corona discharge having apolarity opposite to that carried by thetoner particlecausing the toner to be electrostatically transferred tothesheet. v y The Vyverberggenerator, as attested to" by its widecommercial acceptance, has proven to be an extremely reliable device fortransferring a single toner image to a final support sheet. The termsingle toner image as herein used, is employed in the broad sense todefine an image that is created by means of a single exposure anddeveloping step and the image may include many separate and distinctpieces of information. However corona induced transfer doesnotlenditself readily for use in systems where a multiplicity of toner imagesmust be sequentially tran'sferredto a single support sheet asexemplified by many xerOgraphiccoIOr and Biased roll transfer has beentried with some limited success as a means of controlling theforces'actin'g on the toner during transfer. This type of transfer wasfirst disclosed by Fitch in U. S. Pat. No. 2,807,233 and involved theuse of a metalroll coated with a resilient coating having a resistivityof about/ to 10 cm. Because of the resistivity of the coating, theamount of bias that can be applied to the roll is limited to relativelylow operating values because, at the higher ranges,

the air in and about the transfer zone begins to break down, i.e.ionizes, causing the image to be degradated during transfer. Shelffo inU. S. Pat. No. 3,520,604,

suggests that the resilient coating have a resistivity of between l0l0ohms cm. Here, in order to give the roll the needed resiliency requiredin most practical applications, the coating must be relatively thick. Athick coating of high resistivity acts to build up I a surface charge onthe roll resulting in air breakdown in the transfer region andeventually copy degradation.

, It is therefore an object of this invention to improve -'apparatus forelectrically transferring a toner image from a photoconductivesurface-toa final support sheet. I a;

further object of this invention i's 'to provide a device to bettermatch the speed ofthe support sheet to that of thephotoconductivesurface on which is supported to toned image to betransferred.

efficiently transferred from a photoconductive surface to a singlesheetof final support material. I

- These and other objects of the present invention are I attained bymeans of a biased transfer member being capable of electricallycooperating with a conductive support surface to attract charge tonerparticles from the support surface towardsthe member, the member havinga conductive substrate for supporting a biased "potential thereon, anintermediate blanket placed in contact with the substrate having anelectrical resistivity capable of readily transmitting the biaspotential on the-substrate to the outer periphery of the blanket and arelatively thin outer coating placed over the blanket having anelectrical resistivity to minimize ionization of the atmosphere whenthetransferred member is placed in electrical cooperation with the imagesupport surface and provides a good toner release property enabling thedevice to be cleaned of said toner.

' Fora better understandingas well as other objects and further featuresthereof, reference is had tothe following detailed description of theinvention to be read in connection wherein; I 'FIG. 1 isa schematic viewin partial section illustrating an automatic xerographic reproducingapparatus embodying the present invention; 7 I I FIG. 2 is a perspectiveview inpartial section showing the construction of .a transfer rollembodyingythe teachingsof the present invention that is suitable forwith the accompanying drawings,

' use in the apparatus illustrated inFIG. l; j

' FIG. 3 isv a partial sectional view showinga paper gripping mechanismassociated with the transfer roll illustrated in FIG. 2 with the papergripper extended in a paper stripping position. I

Although the apparatus of the present invention has application in anynumber of xerographic devices in which a plurality of images are to beapplied to a single sheetof support material, it will nevertheless bedis closed, for explanatory reasons, with reference to an automaticmachine having a duplex capability and it should be clear that thisparticular machine environment is in no way intended to limit thepresent invention. Referring now specifically to FIG. 1, the apparatusof the present invention is shown embodied in a drum type automaticxerographic reproducing dicated by means of a motor (not shown). Thedrum basically comprises an outer surface 13 of a photoconductiveinsulating material such as vitreous selenium or the like that is placedupon a grounded conductive substrate 14'. 1

. A uniform electrostatic charge is placed on the photoconductivesurface by means of a conventional corona charging device similar tothat disclosed by Vyverberg in the above noted U. S. patent. Theuniformly charged surface is then moved past an exposure means,generally referenced 17, capable of exposing the charged surface to aflowing light image of the original input scene information to bereproduced thus forming a latent electrostatic image on thephotoconductor. The optical system herein utilized is similar to thatdisclosed in U. S. ,Pat. No. 2,940,358 and is of the type wherein theoriginal input scene information to be reproduced is stored as minifieddata upon a film input 18. A' movable mirror system 19 is positioned inthe optical light path and is arranged to redirect theflowing lightimage of the original onto the bottom portion of the drum surface. Themirror system comprises a plane mirror surface 20 and a roof mirror 21which, in operation, are alternately interposed into the light path ofthe optical system so that each successive image presented to the drumsurface is optically reversed. In operation, the optical means exposesthe photoconductive drum to a first input wherein a right reading latentimage is formulated thereon. Following the formation of the first rightreading latent image, the image is moved past a conventional xerographicdeveloping device 25 wherein the latent image is brought in contact withoppositely charged toner particles and the particles are attracted'intothe imaged areas thus making the image visible. I After development, thenow visible first right reading image is transported on the drum to' atransfer station I 26 where the image is temporarily transferred .to andstored in image configuration upon the surface of an intermediate biasedtransfer roll 30. The transfer roll is arranged to extend transverselyacross the photoconductive drum surface and to move in intimate contacttherewith as shown in FIG. 1. In practice, the. roll, which is initiallyplaced ata relatively high bias potential, is arranged to coactelectrically. with the grounded photoconductive drum to establish anelectrostatic force field. in and about'the contact region. The forcefield is of sufficient strength to attract the charged toner particlesmoving through. this region from the photoconductive surface towards thetransfer member.

Referring now more specifically to FIG. 2, there is shown a cut-awayview of the transfer roll 30 clearly illustrating the internalconstruction thereof. The roll is basically formed upon a rigid hollowcylinder 31 that is fabricated of a conductive metal, such as aluminumor the like, capable of readily responding to a biasing potential placedthereon. Overthe core is placed a rela tively thick intermediate blanket32 of elastomeric material having a hardness of between 15-25durometers. The intermediate blanket is preferably formed of apolyurethane rubber approximately 0.25 in thickness having sufficientresiliency to allow the roll to deform when brought into moving contactwith the photoconductive drum surface to provide an extended contactregion in which the toner particles can be transferredbetween thecontacting bodies. The intermediate blanket should be capable ofresponding rapidly to the biasing potential to electrically impart thecharge potential on the core to the outer extremities of the rollsurface. The blanket therefore should have a resistivity of blanket isplaced a relatively outer coating 33 which is also formed of anelastomeric material being approximately 0.0025 in thickness and havinga hardness in the 65-75 D durometer range. However, in

"order to minimize ionization of the atmospherein and "aboutthe contactregion, it is 'preferredthat the outer coating have a resistivityofabout 3.2 X 10 ohms cm or, alternatively, in a range between 10 and 10"ohm cm. It is further preferred that the outer coating of the rollshould be formulated of a material capable of providing a'relativelysmooth surface exhibiting relatively good mechanical releaseproperties'in respect to the toner materials employed. A polyurethanematerial manufactured by the duPont Company under the tradename Adiprenehas been found .to possess the heretofore mentioned desired propertiesand shows extremely good release characteristics in respect to mostcommercially availabletoners. v

.The transfer roll member is closed atboth ends by means of a pair ofdielectric end caps 35, 36 which serveto electrically isolate thetransfer roll member from the supporting machine frame. Segmented shafts37 are secured in both end caps and are mounted in coaxial alignmentwith the cylindrical core 31. The shafts, in turn, are joumaled forrotation in the machine frame in bearing means provided (not shown) sothat the outer surface of the roll continually moves'through thetransfer zone in contact with the photoconductive surface 13. A pulley38, operatively connected to the machines main drive system, is securedto one end of the shaft and causes the transfer roll to be rotated inwith the moving shown in FIG. 1, a commutating brush 41, which iselectrically connected to a suitable source of DC power 42 viaelectrical connector 43, is arranged to ride in contact with theoutersurface of the commutator ring and provides a moving contact by whichtheconductive core is electrically connected to the biasing source. Thetransfer force field associated with the electrically isolated roll isdependent upon the establishment of a voltage contrast between the rolland the photoconductor. The strength of the field is proportional to theinitial charge placed on the roll and inversely proportional to thedistance between the two coacting bodies. Initially, the roll is biasedto about 3,500 volts DC, the polarity of which is, of course, oppositeto that of the charged toner particles, whereby the first imagedelivered into the transfer zone is transferred, in image configuration,from the photoconductor to the surface of the-transfer roll.

Subsequent to the formation of the first right reading image upon thedrum, a second area on the photoconductive surface thereof is againuniformly charged by I means of the charging corotron 15. This second psstatic image, roof mirror 21 is interposed into the optical light pathof the system'replacing mirror 20. This wrong-readinglatentelectrostatic image is then transported on the moving drum surface tothe development station -23'and the second'image is made visible in amanner similarto that herein described in reference to the first rightreading image. I

The time sequence 'of charging, exposing and- 1 developing the twooppositely .reading images on the drumsurfac e is controlled inpredetermined timed rela- 82, preferably paper, are forwarded from asupply bin 'tionf by means of ,the machine-control logic circuitry ;(notshown). Of course, the particular selection of the 6 ln operation,sheets of individual support material orthelikeintoa sheet'receivingstation 83 (FIG. 1) by means of a feed roll assembly27. At this time,tabs 84, (FIG. 3) on the lifting arm are elevated slightly above theroll surface and the leading edge of the sheet is driven into alignmentagainst stop face 85.v Once aligned,the tabelement is caused to movedownwardly thus locking the sheet against recess surface 87 on the roll.When in the sheet locking position, the entire gripping mechanism issufficientlyretractedbelow the "roll surface to allow the roll to'movefreely through the times sequence of operation may be dependent 'on manyfactors, such as the location ofsthe various processing stations aroundthe drum surface, thelength and velocity of the image storage memberrelative to .sthezsiz e of the drum surface, and-the like.Eorconvenienceof illustration, however, the circumference of thetransfer .roll -isherein deemed to be one'half that of the,photoconductive drum. Byrotating the two-members"at-ithe'lsamePQfiPheral speed, the first image,

which has been transferred-to the transfer -roll,'--is trans-.ported'around -the circularpath of travel transcribed by the drum andwill arrive atthe transfer station at ap-.

proximately the same time as the second developed image carried on thephotoreceptor. Accordingly, the --leading edges of the two images lyingrespectively on the storage drum and the xerographic drum surface,

confront each other atapproximately the same mor'nent-in-ztime.

contactor transfer zone. v v

, With'the support sheet 82 secured to the roll surface over the firstimage the first image is recirculated once again through the transferorcontact region in synchronization with thesecond image carried on thelphotoconductive drum. The introduction of an added dielectric, suchasapaper sheet, into the contact region I usually: requires thatthetransfer bias be reduced'in from the photoconductor to the outsidesurface of the Prior to bringing the two toner images together withinthe contact region, a sheet of "final" support material, such as paperor the like, is secured to the transfer roll member in a manner whereinthe sheet overlies the first image supported' ther'eon. "A sheet sheet.I

After transfer, the support sheet is moved onthe roll surface to aregion of low voltage contrast wherein there-is positioned a coronagenerator 55 similar to that described in the previously noted Vyverbergpatent. A

region of low .voltage contrast is a regionwherein the gripping-deviceis providedwithin the roll to properly align and secure individualsheetsof material to theroll surface. Basically, two sheet aligning andgripping assemblies 60 (516.3.) are supported'in spaced parallelalignment within the roll-to act ,upon the two leading edge corners of asupport sheet that is broughtinto operative communication therewith.Each assembly is made up of two components, alever arm component biasroll surface does not electrically communicate with another voltagesource. it should be understood, that the term -voltage sourcej asherein used is broad enough to' include a .groundedjbody or the like.The

corona generator is dapted o' apply corona to the top and a liftingcomponent 64 .tha't are supported upon a common base plate 65 by meansof a mounting bracket 66. The base plate is rigidly affixed to theinterior walls of the roll and is arranged to move in unison with theroll member. I

Mounting bracket 66 also serves to rotatably support a control shaft 67which runs longitudinally across the interior of the roll and eittendsthrough the end cap 36 (FIG. 2). Each of the lever, arm components arerotatably secured to bracket 66 by means of a pin 68 and the armsarranged to rotate freely in openings '69 I provided in the rollsurface. Lifting elements '64 are secured to the control shaft 67 andmove in accordance therewith. A 'cam face 70 is machined on the liftingele .ment and is forced to ride in contact with the bottom surface ofthe lever arm by means of a spring 71 so that the lifting arm is raisedand lowered in response to the movement of the control, shaft. Theportion of the control shaft that extends beyond end cap 36 is providedwith a cam followed 78 arranged to ride in contact with 1 impart apredetermined motion- Ea profile surface 79 to to thelever arm.

side of'the support sheet'of a polarity to cause the first image,tha't'is, the image in contact with the roll surface-to be transferredfrom the roll to the bottom side of the support sheet. Alternately, thebias potential on the roll can be removed prior to the corona inducedtransferstep. 1

With the two toner images thus electrostatically adhering t0 Opp sitesides of the support sheet, the sheet is once again moved on the rollsurface into the sheet receiving station 83. Here, the lever arm 63 ofthe gripping mechanism is moved to a fully extended position, as shownin FIG. 3, causing the .sheet to be elevated 'well above the rollsurface. As the-roll continues to move in the direction indicatedptheelevated sheet is carried over a stripping bar 89 which guides the sheetinto a fuser assembly 90.v The sheet is advanced through thefuserassembly by means of a transport 91 and the images are permanentlyfixed to both sides of the support 'sheet. The now duplexed copies aretaken from the fuser and stored in a collecting tray 83.

' Finally, the rotating photoconductive surface as it moves out oftransfer station is brought into operative communication with a fibrousbrush member 50 that is moving at'a speed sufficient to dislodge anyresidual toner remaining on the drum surface after the transferoperation. The residual toner is collected and removed from "the machineenvironment by means of conventional apparatus'known and used in theart.

changes as may come within the scope of the following claims. a I

What is claimed is: v t 1. A transfer member forv electricallycooperating with a conductive support surface to electrically attractcharge particles from the support surface towards the member including,I I I va conductive substrate for supporting a uniform bias I potentialthereon,

an intermediate resilient blanket placed in contact with said substratehaving an electrical resistivity such that the blanket is capable oftransmitting said bias potential on said substrate to the outerperiphery of said blanket, and I an outer coating placed oversaidblanket having an electrical resistivity to minimize ionization ofthe surrounding atmosphere when said transfer member is placed inelectrical cooperation with said support surface.

2. The transfer member of claim 1 wherein said intermediate blanket isformed of an elastomeric material having a resistivity of between and 10ohms cm.

3. The transfer member of claim 2 wherein said outer coating isformedvof an elastomeric material having a resistivity of between 10 and10 ohms cm.

4. The transfer member of claim 3 wherein said sub strate is formed of aconductive metal in the shape of an endless belt.

5. A transfer roll for electrically cooperating with a photoconductiveplate when brought into contact therewith to attract charged tonerparticles from the plate toward the roll including a rigid cylindricalcore or electrically conductive material,

.rneans.to connect said core to a biasing source whereby a uniformbiasing potential is placed upon said core,

a resilient intermediate blanket placed over said I core, in contacttherewith, having an electrical re- I sistivity such that the blanket iscapable of trans- Imittingsaid bias potential from said conductive coreto the outer periphery of said blanket,

an outer resilient coating placed over said blanket having a resistivityto minimize ionization of the surrounding atmosphere in and about thezone of contact between the transfer roll and the photoconductive plate.I

6. The transfer roll of claim 5 wherein said intermediate blanket isformed of a polyurethane material having a resistivity of between 10 and10 ohms cm.

7. The transfer roll of claim 6 wherein said outer coating is formed ofa, polyurethane material having a resistivity of between l0 and 10 ohmscm.

8. The transfer roll of claim 7 further including dielectric end capsfor rotatably supporting and electrically isolating said transfer roll.

9. The apparatus-of claim 8 further including sheet gripping means tosecure a sheet of final support material to the outer surface of saidtransfer roll.

10. The apparatus of claim 7 wherein said intermediate blanket has ahardness of between 15 and 25 durometers, Shore A.

1. The apparatus of claim 10 wherein said outer coating has a hardnessof between 65 and durometers, Shore D. I

1. A transfer member for electrically cooperating with a conductivesupport surface to electrically attract charge particles from thesupport surface towards the member including a conductive substrate forsupporting a uniform bias potential thereon, an intermediate resilientblanket placed in contact with said substrate having an electricalresistivity such that the blanket is capable of transmitting said biaspotential on said substrate to the outer periphery of said blanket, andan outer coating placed over said blanket having an electricalresistivity to minimize ionization of the surrounding atmosphere whensaid transfer member is placed in electrical cooperation with saidsupport surface.
 2. The transfer member of claim 1 wherein saidintermediate blanket is formed of an elastomeric material having aresistivity of between 109 and 1010 ohms cm.
 3. The transfer member ofclaim 2 wherein said outer coating is formed of an elastomeric materialhaving a resistivity of between 1013 and 1015 ohms cm.
 4. The transfermember of claim 3 wherein said substrate is formed of a conductive metalin the shape of an endless belt.
 5. A transfer roll for electricallycooperating with a photoconductive plate when brought into contacttherewith to attract charged toner particles from the plate toward theroll including a rigid cylindrical core or electrically conductivematerial, means to connect said core to a biasing source whereby auniform biasing potential is placed upon said core, a resilientintermediate blanket placed over said core, in contact therewith, havingan electrical resistivity such that the blanket is capable oftransmitting said bias potential from said conductive core to the outerperiphery of said blanket, an outer resilient coating Placed over saidblanket having a resistivity to minimize ionization of the surroundingatmosphere in and about the zone of contact between the transfer rolland the photoconductive plate.
 6. The transfer roll of claim 5 whereinsaid intermediate blanket is formed of a polyurethane material having aresistivity of between 109 and 1010 ohms cm.
 7. The transfer roll ofclaim 6 wherein said outer coating is formed of a polyurethane materialhaving a resistivity of between 1013 and 1015 ohms cm.
 8. The transferroll of claim 7 further including dielectric end caps for rotatablysupporting and electrically isolating said transfer roll.
 9. Theapparatus of claim 8 further including sheet gripping means to secure asheet of final support material to the outer surface of said transferroll.
 10. The apparatus of claim 7 wherein said intermediate blanket hasa hardness of between 15 and 25 durometers, Shore A.
 11. The apparatusof claim 10 wherein said outer coating has a hardness of between 65 and75 durometers, Shore D.